Our projects have focus on the biology, cell biology, molecular biology, and biochemistry of activated lymphocytes, cells that are a component of the immune system, have been used for treating cancer, and participate in the cellular rejection response against cells, tissues or organs from humans (e.g., human, or allogeneic, tissues) and species other than human (xenogeneic). We continue our study of how immune cells that kill other cells (cytolytic or cytotoxic cells) are regulated by chemical oxidation-reduction conditions and have found that certain chemicals that generate a reducing environment are necessary for optimal activity. In the case of the immune response to xenogeneic cells, we have found that this response is regulated by oxidation-reduction and another chemical mediator, nitric oxide, also modulates the response. We have also shown that certain human cytokines, or cellular hormones, modulate the response of human cells against pig cells, and that the most potent human cell in this response belong to the population known as natural killer cells. We have shown that a cell surface molecule known as Fas ligand when expressed on the surface of pig cells protects them from being killed by human cells that are otherwise very efficient cytotoxic cells. Finally, we have also shown that certain porcine adhesion molecules (e.g., E-selectin or CD62E) are recognized by human cytolytic cells and therefore may be important in rejection of porcine xenografts.